From c3be846008a1ae6aba05d3c4f83b8787e41dd239 Mon Sep 17 00:00:00 2001
From: rillig <rillig@NetBSD.org>
Date: Sun, 12 Sep 2021 17:30:53 +0000
Subject: [PATCH] lint: track down wrong function type in abstract type

---
 tests/usr.bin/xlint/lint1/msg_347.c   | 16 +++++++++++++++-
 tests/usr.bin/xlint/lint1/msg_347.exp |  4 ++++
 usr.bin/xlint/lint1/decl.c            | 14 +++++++++++---
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/tests/usr.bin/xlint/lint1/msg_347.c b/tests/usr.bin/xlint/lint1/msg_347.c
index 1980efe667a3..1619096c88ab 100644
--- a/tests/usr.bin/xlint/lint1/msg_347.c
+++ b/tests/usr.bin/xlint/lint1/msg_347.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: msg_347.c,v 1.1 2021/09/12 16:28:45 rillig Exp $	*/
+/*	$NetBSD: msg_347.c,v 1.2 2021/09/12 17:30:53 rillig Exp $	*/
 # 3 "msg_347.c"
 
 // Test for message: redeclaration of '%s' with type '%s', expected '%s' [347]
@@ -27,3 +27,17 @@
 void function_parameter(void *, double *(void *, int));
 /* expect+1: error: redeclaration of 'function_parameter' with type 'function(pointer to void, pointer to function(pointer to void, int) returning pointer to double) returning void', expected 'function(pointer to void, int) returning void' [347] */
 void function_parameter(void *fs, double *func(void *, int));
+
+
+/* expect+1: warning: struct last_arg never defined [233] */
+struct last_arg;
+/*
+ * FIXME: The following error is completely wrong.
+ * There is no argument that has 'struct last_arg', there are only pointers
+ * to it.
+ */
+/* expect+2: error: '<unnamed>' has incomplete type 'incomplete struct last_arg' [31] */
+/* expect+1: previous declaration of last_arg_struct [260] */
+void last_arg_struct(double, double *(struct last_arg *));
+/* expect+1: error: redeclaration of 'last_arg_struct' with type 'function(double, pointer to function(pointer to incomplete struct last_arg) returning pointer to double) returning void', expected 'function(double, incomplete struct last_arg) returning void' [347] */
+void last_arg_struct(double d, double *fn(struct last_arg *));
diff --git a/tests/usr.bin/xlint/lint1/msg_347.exp b/tests/usr.bin/xlint/lint1/msg_347.exp
index 03fee641e07a..b6d5fd7f1f30 100644
--- a/tests/usr.bin/xlint/lint1/msg_347.exp
+++ b/tests/usr.bin/xlint/lint1/msg_347.exp
@@ -1,2 +1,6 @@
 msg_347.c(29): error: redeclaration of 'function_parameter' with type 'function(pointer to void, pointer to function(pointer to void, int) returning pointer to double) returning void', expected 'function(pointer to void, int) returning void' [347]
 msg_347.c(27): previous declaration of function_parameter [260]
+msg_347.c(41): error: '<unnamed>' has incomplete type 'incomplete struct last_arg' [31]
+msg_347.c(43): error: redeclaration of 'last_arg_struct' with type 'function(double, pointer to function(pointer to incomplete struct last_arg) returning pointer to double) returning void', expected 'function(double, incomplete struct last_arg) returning void' [347]
+msg_347.c(41): previous declaration of last_arg_struct [260]
+msg_347.c(33): warning: struct last_arg never defined [233]
diff --git a/usr.bin/xlint/lint1/decl.c b/usr.bin/xlint/lint1/decl.c
index 3ac7eb02d37b..9405fdbe3871 100644
--- a/usr.bin/xlint/lint1/decl.c
+++ b/usr.bin/xlint/lint1/decl.c
@@ -1,4 +1,4 @@
-/* $NetBSD: decl.c,v 1.236 2021/09/12 16:28:45 rillig Exp $ */
+/* $NetBSD: decl.c,v 1.237 2021/09/12 17:30:53 rillig Exp $ */
 
 /*
  * Copyright (c) 1996 Christopher G. Demetriou.  All Rights Reserved.
@@ -38,7 +38,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID) && !defined(lint)
-__RCSID("$NetBSD: decl.c,v 1.236 2021/09/12 16:28:45 rillig Exp $");
+__RCSID("$NetBSD: decl.c,v 1.237 2021/09/12 17:30:53 rillig Exp $");
 #endif
 
 #include <sys/param.h>
@@ -1398,11 +1398,19 @@ add_function(sym_t *decl, sym_t *args)
 		dcs->d_next->d_func_args = args;
 	}
 
+	/*
+	 * XXX: What is this code doing on a semantic level, and why?
+	 * Returning decl leads to the wrong function types in msg_347.
+	 */
 	tpp = &decl->s_type;
 	while (*tpp != NULL && *tpp != dcs->d_next->d_type)
+		/*
+		 * XXX: accessing INT->t_subt feels strange, even though it
+		 * may even be guaranteed to be NULL.
+		 */
 		tpp = &(*tpp)->t_subt;
 	if (*tpp == NULL)
-	    return decl;
+	    return decl;	/* see msg_347 */
 
 	*tpp = tp = getblk(sizeof(*tp));
 	tp->t_tspec = FUNC;